A scanning tunneling microscope (STM) designed for biological application and operating at ambient pressure is described. It is combined with a light microscope, monitoring the specimen through a transparent support, which is used to search for specimen areas of interest. Glass or mica coated with a thin conductive layer (e.g., carbon) are used as a specimen support. The STM itself, is essentially a Besocke-type STM; modifications include a convenient and reliable mechanism for sample approach to the tip (z adjustment). (3 References)